In OVCAR3 cells, IFNAR1/IFNAR2-RNAi (80-90% knock down) or IRF9-RNAi (80% knockdown) completely inhibited the antiproliferative activity of IFN-alpha. On the other hand, the IRF9-RNAi demonstrated no inhibition of the antiproliferative activity of IFN-gamma. These results suggest that IFN-alpha signals through IFNAR1/IFNAR2 and utilizes IRF9 to elicit the anti-cancer activity in OVCAR3 cells. Furthermore, TRAIL gene expression (related to apoptosis) was inhibited by IFNAR1-RNAi or IRF9-RNAi, but not by Stat1-RNAi following IFN-alpha treatment, suggesting that induction of the TRAIL gene plays a role in eliciting the antiproliferative activity of IFN-alpha. Previously we reported that low concentrations of interferon (IFN) activated monocytes (105/microtiter well) exert near eradicative cytocidal activity against low concentrations of several human tumor cells (103-4/mictotiter well) in vitro. This year we first confirmed strong cytocidal activity against seven human tumor cell lines. Then, to model larger in vivo tumors, we increased the target cell concentration one hundred-fold (105 cells) and found that increasing the tumor cell concentration increased the concentration of IFNs required for eradication by over 100 fold and the required concentration of monocytes by 10 fold. Thus in vitro modeling of high concentrations of target cells required high concentrations of monocytes and IFNs to approach tumor cell eradication. Preliminary in vivo studies on human ovarian tumors in immunosuppressed mice showed significant tumor eradication and enhanced survival after treatment with human monocytes and interferon alpha.